What is it called when you measure the height of a tree using its shadow?

Question

You have your height, the height of your shadow and the height of the tree's shadow. You want to find out how tall the tree actually is, how do you do that? And what is it called? [The property or mathematical term for it.]

Answer 1

It's called the pathegorean theorm.

Answer 2

Ratios?

Your height/your shadows height = tree height/tree shadow height

Answer 3

trigonometry my friend